The present invention relates to fiber reinforced plastic pipes (FRP pipes) and filament winding apparatuses, and, more particularly, to FRP pipes that have a helix winding layer and a hoop winding layer and to filament winding apparatuses that manufacture the FRP pipes.
A filament winding process is used to efficiently fabricate an FRP pipe or container. Generally, the process uses a filament winding apparatus that has a chuck mechanism and a fiber feeding mechanism. The chuck mechanism holds shafts that project from opposite ends of a mandrel and rotates the mandrel at a predetermined speed. The fiber feeding mechanism feeds a fiber strand, which is impregnated with resin, to the mandrel and winds the fiber strand around the mandrel body. To increase the productivity of the process and improve the quality of the product, it is preferred that the fiber strand be wound around the mandrel body in a spread state.
Japanese Laid-Open Patent Publication No. 11-286056 describes an apparatus that spreads a fiber strand and winds the spread fiber strand around a mandrel. The fiber strand is spread regardless of the angle at which the fiber strand is wound to the mandrel. Referring to FIG. 23, the apparatus includes a mandrel 91, a resin impregnating tank 92, and a guide roller 94. The mandrel 91 rotates and moves reciprocally in the axial direction. The guide roller 94, which moves relative to the resin impregnating tank 92, guides a fiber strand 93 from the resin impregnating tank 92 to the mandrel 91. The resin impregnating tank 92 and the guide roller 94 are arranged on a table 96, which is supported by a support shaft 95. The table 96 and the guide roller 94 move in accordance with the angle at which the fiber strand 93 is wound to the mandrel 91 so that the fiber strand 93, which is guided by the guide roller 94 from the resin impregnating tank 92 to the mandrel 91, is straightened.
Japanese Laid-Open Patent Publication No. 8-276504 describes an apparatus that has a feed eye 97, as shown in FIG. 24. The feed eye 97 includes a plurality of slits 97a to simultaneously wind a plurality of fiber strands 93 around a mandrel 91. The feed eye 97 is secured to a base plate 98. The base plate 98 rotates about the fiber strands 93 fed to the slits 97a. The base plate 98 also pivots about a line perpendicular to a plane that includes the fiber strands 93.
Japanese Laid-Open Patent Publication No. 6-254974 describes an apparatus having a pad. The pad has an arcuate surface for rubbing fiber strand, which is impregnated with resin, when the fiber strand is wound around the mandrel. This defoams the resin and removes excessive resin from the fiber strand.
The apparatus of Japanese Laid-Open Patent Publication No. 11-286056 cannot simultaneously wind multiple fiber strands 93 around the mandrel 91. In contrast, the apparatus of Japanese Laid-Open Patent Publication No. 8-276504 winds simultaneously helically winds multiple fiber strands 93 around the mandrel 91 to form a helix winding layer. However, when the base plate 98 and its drive mechanism of the base plate 98 reaches one end of the mandrel 91 where the winding direction of the fiber strands R is reversed, the base plate 98 and a drive mechanism overhang from the mandrel 91. This enlarges the space required to enable the reciprocating movement of the base plate 98.
Further, to fabricate an FRP pipe having the desired property, a hoop winding layer, which is formed by winding a fiber strand around a mandrel in a direction substantially perpendicular to the axis of the mandrel, may have to be formed on a helix winding layer. Alternatively, a helix winding layer may have to be formed on a hoop winding layer. However, the aforementioned apparatuses cannot switch between the two types of windings. In addition, a pair of hoop winding layers may have to be formed on a helix winding layer at opposite ends of the FRP pipe. If such a case, to increase productivity, it is preferred that each fiber strand not be cut when completing the formation of one hoop winding layer at one end of the pipe and shifting to the other end of the pipe to form the other hoop winding layer. To form two hoop winding layers at opposite ends of an FRP pipe, a fiber strand continuously extending from one hoop winding layer is helically wound around the underlying helix winding layer as a crossing thread until it reaches the other end of the pipe where the other hoop winding layer is formed. Further, in some cases, after the hoop winding layers are formed, another helix winding layer may be formed on the hoop winding layers.
Also, in the apparatus of Japanese Laid-Open Patent Publication No. 6-254974, only part of the mandrel is faced toward the pad. In other words, the pad does not cover the entire circumference of the mandrel. Thus, the pad cannot sufficiently remove resin from the fiber strand.
In addition, an organic fiber that is not impregnated with resin, such as a polyester fiber, may be wound around an outermost layer of the resin-impregnated fiber strands to fabricate an FRP pipe with a relatively high fiber volume content (Vf). This removes excessive resin from the fiber strands. However, in such case, the form of the crossing thread may appear through the organic fiber depending on the winding angle of the crossing thread. This is not desirable with regard to the appearance of the FRP pipe.
Accordingly, it is a first objective of the present invention to provide an FRP pipe that improves productivity even if the FRP pipe includes a helix winding layer and a pair of hoop winding layers that are formed at opposite ends of the pipe. It is a second objective of the present invention to provide an optimal filament winding apparatus for fabricating an FRP pipe. It is a third objective of the present invention to provide a filament winding apparatus that efficiently removes excessive resin from a fiber strand.
To achieve the above object, the present invention provides an FRP pipe including a helix winding layer formed by cylindrically winding reinforced fibers. The helix winding layer has two ends and an axis, and the reinforced fibers forming the helix winding layer are wound at an angle relative to the axis. Hoop winding layers are formed at each end of the helix winding layer by winding reinforced fibers at the ends. The hoop winding layers are formed from the same continuous reinforced fibers.
A further perspective of the present invention is a filament winding apparatus for winding fiber strands to a cylindrical wound subject while rotating the wound subject. The apparatus includes a winding unit moved reciprocally along an axial direction of the wound subject. The winding unit winds fiber strands, which are impregnated with resin, around the wound subject. The winding unit includes a helix winding head for simultaneously winding fiber strands around the wound subject, a hoop winding head for simultaneously winding a fiber strand around the wound subject, a helix fiber spreading portion for spreading the fiber strands wound around the wound subject by the helix winding head, and a hoop fiber spreading portion for spreading the fiber strand wound around the wound subject by the hoop winding head.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.